Simplify the following expression: $q = \dfrac{3}{4r} - \dfrac{1}{6r}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $4r$ and $6r$ $\lcm(4r, 6r) = 12r$ $ q = \dfrac{3}{3} \cdot \dfrac{3}{4r} - \dfrac{2}{2} \cdot \dfrac{1}{6r} $ $q = \dfrac{9}{12r} - \dfrac{2}{12r}$ $q = \dfrac{9 -2}{12r}$ $q = \dfrac{7}{12r}$